This application relates generally to spark plugs for internal combustion engines and, more particularly, to a jamb nut to insulator interface that reduces loads on the spark plug insulator.
Traditional spark plug construction includes an annular metal casing having threads near one end and a ceramic insulator extending from the threaded end of the metal casing as well as beyond the opposite end of the metal casing. A central electrode extends through the insulation and is exposed near the threaded end. The central electrode is also electrically connected to a terminal that extends from an opposite end of the insulator. The terminal is configured to be attached to a spark plug ignition wire.
The force applied to seal the spark plug in the head of an engine block is the result of torque transmitted to the threaded metal casing; hence, the threaded portion of the metal casing must be sturdy and of substantial size. A portion of the metal casing is formed to have a jamb nut that is configured to be engaged by a socket tool to provide the torque to the threaded portion. The threaded portion is located away from the jamb nut which is engaged by the socket tool.
To facilitate the controlled and efficient exhaust of gases from a combustion chamber, the valves are sometimes increased in size. This may cause a decrease in the combustion chamber wall area available to threadedly receive the spark plug, which in turn may necessitate a decrease in the size of the bore receiving the spark plug, and in some instances an increase in the overall length of the spark plug. Accordingly, the spark plugs associated with these reduced size bores will also have a corresponding reduced diameter.
The decrease in the diameter of the spark plug may reduce the spark plugs ability to hold onto its ground shield during removal. A higher strength steel jamb nut may be used to combat this problem however, assembling a higher strength steel jamb nut to the insulator will result in higher loads being applied to the insulator during assembly.
Accordingly, the inventor herein has recognized that it is desirable to provide a jamb nut to insulator interface that reduces loads upon the insulator.